Lin28 is a highly conserved RNA-binding protein that has an important role in human body development, metabolism, and tumorigenesis. Previous studies have found that the activation of Lin28 can suppress the maturity of let-7 miRNA in stem cells and promote the proliferation of stem cells by upregulating cell-cycle related genes, such as cyclins A and B. Other mechanisms underlying the activation of Lin28 can selectively block the processes of pre-let-7 miRNA in embryonic stem cells and ultimately promote tumori-genesis. In addition, Lin28 affects the occurrence, development, and prognosis of cancer by inhibiting the differentiation and maturation of miRNA and by moderating the expression of some cell-cycle related genes. Lin28 has an important function in the tumor's tolerance of chemotherapy and radiotherapy. We review the physiological function of Lin28 in tumors and its function in tumor treatment.